Conventionally, a system has been implemented which creates a stereoscopic image artificially using successfully a visual function of a human being for stereoscopic image. Such stereoscopic image system is designed to pick up an image of the same object by two television cameras placed corresponding to human binocular parallax and to supply image information for right and left eyes obtained by these two television cameras, to right and left eyes of a viewer, respectively. A concrete method therefor is shown in Japanese Patent Laying-Open Gazette No. 160292/1985 in which image information for respective eyes are alternately supplied to a television receiver for each field, and in relation to the supplying operation, light shutters of eyeglasses (special eyeglasses for stereoscopic view on which light shutters are provided for left and right eyes, respectively) are activated alternately. Another method has been also considered in which image information for both eyes are displayed on a screen at the same time using beams having different planes of polarization and the displayed pieces of image information are viewed by polarizing eyeglasses (a polarization axis for a right eye coincides with a plane of polarization of image information for a right eye and a polarization axis for a left eye coincides with a plane of polarization of image information for a left eye).
The above described stereoscopic image system requires special eyeglasses because the image looks doubled on a displayed screen when viewed through a direct visual observation. In effect, however, viewers do not always have eyeglasses. Especially, when one television receiver is viewed by many people, such problem is likely to arise. Therefore, the stereoscopic image system is preferably designed not only to display a stereoscopic image but also to display a conventional TV image.
There are two types of the above described stereoscopic systems; one receives a broadcasting signal of a stereoscopic image to display the stereoscopic image, and the other reproduces stereoscopic image information recorded in a recording medium by a player to display the stereoscopic image. At present, the latter is more popular which reproduces the recording medium, especially the stereoscopic video disc record by video disc player to display the stereoscopic image. If the stereoscopic video disc record is used as an image information source, the stereoscopic video disc record is required to be adaptable to reproduction of both stereoscopic image information and two dimensional image information in order to satisfy the above described requirement, that is, compatibility between stereoscopic reproduction and plane reproduction.
A stereoscopic video disc record of VHD system is published in a journal, "Television Technique", pp. 20-23, published by Denshi Gijutsu Shuppan Kabushiki Kaisha (Electron Technology Publishing Co., Ltd.), Jan. 1, 1986, in which not only stereoscopic image information but also two dimensional image information can be reproduced. This stereoscopic video disc record appeared in the prior art is constructed to have image information recorded on spiral recording tracks. The recording tracks are divided into four recording regions by 90 degrees per rotation of the stereoscopic video disc record and the image information for a right eye or a left eye for 1 field is recorded on each recording region. The pieces of image information for right and left eyes to be reproduced at the same time in the same field are recorded in parallel in the recording regions which are next adjacent to each other in a radial direction of the stereoscopic video disc record. Therefore, if the next adjacent recording tracks in a radial direction are reproduced at the same time, the pieces of image information for a right eye and the image information for a left eye can be reproduced at a synchronized timing, whereby the stereoscopic image can be reproduced. On the other hand, if reproduction is performed by repeating jumps to the adjacent recording regions with the direction to jump being inverted for each 1/4 rotation of the stereoscopic video disc record, the image information only for a right eye or only for a left eye can be reproduced in series, whereby a two dimensional image can be reproduced.
However, the above described stereoscopic video disc record requires many image memories and a large-scale editing system because original image information next adjacent in a time base direction cannot be recorded in that order.
Since the information is reproduced by a reproducing stylus, when the adjacent recording tracks are reproduced at the same time, two reproducing stylus must be placed very close, which makes it difficult to manufacture a pickup. In addition, in case of simultaneous reproduction, one track jump per revolution of the stereoscopic video disc record becomes indispensable with the result that a complicated mechanism to jump is required in the video disc player.
Furthermore, in case of simultaneous reproduction, since the pieces of image information for right and left are provided alternately for every two fields by two reproducing stylus, a mechanism for switching the right and left image information is necessary in the video disc player, which makes the structure complicated.
When the two dimensional image is reproduced using the above described stereoscopic video disc record, a track jump must be performed for every 1/4 revolution, whereby a mechanism for the track jump becomes necessary in the video disc player. Therefore, it is not compatible with a conventional video disc player which is for reproduction of a two dimensional image and have no such a mechanism to jump.
In addition, since the recording tracks on the stereoscopic video disc record are divided into four recording regions by 90 degrees per revolution to record the image information as described above, the image information must be always recorded at constant angular velocity. However, the amount of information which can be recorded on the same record becomes less when recorded at constant angular velocity compared with that recorded at constant linear velocity. Particularly, in the stereoscopic video disc record in which two pieces of image information for right and left are recorded for one field, the recording time is limited to one half as compared with the video disc record in which conventional two dimensional image information is recorded, so that the method of recording at constant linear velocity is preferable because it can record more information.